Extremely high frequency or EHF is the highest radio frequency band and runs the range of frequencies from 30 to 300 GHz. The frequencies in this band have a wavelength of ten to one millimeter, giving it the name millimeter band or millimeter wave (mmWave). In high frequency mmWave circuits, the wavelengths involved are shorter compared to the wavelengths of lower frequencies, which are more commonly used. Thus, the loss per unit length is higher due to radiation, scattering and absorption. Millimeter wave signals, thus, are extremely sensitive to manufacturing inaccuracies. In order to overcome these difficulties, high quality expensive materials and technologies (e.g., ceramic substrates or organic buildup technology) is used that have low absorption and very low manufacturing inaccuracies. In addition, conventional mmWave packages use complex assembly processes.
Currently, many electronic package standards exist in the electronic industry. The vast majority of these packages are capable, however, of supporting only low frequency signals, while state of the art packages support up to 50 GHz signals relying on Surface Mount Technology (SMT) I/O to deliver the signal from the package to a printed transmission line on the electronic circuit board.
Commercial electronic packages for higher frequencies (above 50 GHz) usually rely on a rectangular waveguide interface either in a package for a single chip or in a multi-chip module with an integrated waveguide transition. These waveguide interfaces must be mounted using screws to other waveguide interfaces (such as to other modules or antenna) which increases the package's size and complicates the transmission of low frequency signals to the electronic circuit board.
Today, SMT packages are an industry standard with an established manufacturing procedure which enables low cost production. SMT packages allow ease of mounting on electronic circuit boards under an automated reflow soldering process without the need of mechanical connectors. Their small dimensions make it possible to make high density electronic circuit boards with many different components linked by a network of printed wires and transmission lines. Despite the advantages described above, SMT packages have two main drawbacks in the high frequency bands such as mmWave that cause high electrical losses.
A first drawback is that SMT packages include printed transmission lines such as microstrip or strip lines which exhibit high loss at high frequencies compared with waveguides, and thus a waveguide interface is preferred at those frequencies. A second drawback is that it is difficult to control the precise mounting location of the SMT package on the electric circuit board by means of reflow soldering. Thus, at least half the width of the component termination must be placed on the solder landing. This is a reasonable constraint when working with low frequency signals. When working with mmWave frequencies, however, small inaccuracies in printed transmission lines become significant and can cause high loss and radiation. Due to these two drawbacks, SMT packages are rarely used above 50 GHz.
Contrary to printed transmission lines such as microstrip and strip-lines, waveguides do not exhibit significantly higher loss at higher frequencies. Another benefit of waveguides is that the transmission between two waveguides is hardly affected by inaccuracies in their connection. Waveguide connections have three distinct drawbacks. The first drawback is that connecting a waveguide to a waveguide requires manual labor using screws with a large flange which also significantly enlarges the package size. The second drawback is the need to include more connectors in the package (besides the waveguide flange) in order to deliver low frequency signals, DC supplies, grounds, etc. from the package to the electrical circuit board. The third drawback is the high price of the package due to the expensive waveguide mechanism.
There is thus a need for mmWave packages that can be constructed from inexpensive, common materials and technology, that exhibit low loss and good heat dissipation and that can be manufactured using simple assembly processes.